This invention relates to a control method for detecting an irregularity in the valve-timing changeover for internal combustion engines that have selectable modes of valve-timing operation.
There has been known heretofore from the Japanese Examined Patent Application Publication No. Tokkosho 49-33289 an engine in which a cam shaft provided with a high-speed cam and a low-speed cam is shifted in the axial direction by activating cylinder operation to change over valve timing as desired between a low-speed valve timing at which the intake and exhaust valves are opened and closed by the low-speed cam and a high-speed valve timing at which the intake and exhaust valves are opened and closed by the high-speed cam wherein the changeover of the valve timing is made by opening and closing operation of valve means that control charging oil to and discharging oil from the activating cylinders.
When a hydraulically operated changeover mechanism is used to change over the valve timing as described in the foregoing, sometimes the valve means is not able to provide the predetermined hydraulic pressure changes as expected when instructed to open or close due to sticking of the valve means caused by foreign material clinging thereto or oil leakage or the like, with the result that the valve timing is not changed over normally. It therefore is desirable that a fail-safe arrangement be provided to cope with such a situation which arrangement may including, for example, an alarm to give out a warning, a signal to decrease fuel supply or invalidate the control action for changeover of the valve timing, or the like.
It is, therefore, an object of t he present invention to provide an irregularity-detecting method for accomplishing a desirable fail-safe control in a valve-timing changeover mechanism.